In the construction industry, it is frequently necessary to lay a large area of concrete. Such areas can include, for example, foundations for buildings, floors, driveways, sidewalks, ramps, etc.
Concrete exhibits characteristics of strength in compression but is poor in tension. To increase strength in tension, it is common practice to prepare a grid of reinforcing bars and then to pour concrete over and around the grid whereby the reinforcing bars improve the strength the poured concrete. After the wet concrete has been poured over and around the grid of reinforcing bars, it is common practice in the art to vibrate the concrete to remove air and voids from the poured mix. In this manner, when the concrete hardens, the slab will be more compact and undesirable pockets within the hardened concrete are avoided and the integrity of the concrete is not compromised.
The most common form of concrete vibrator comprises a metal cylinder within which a shaft carrying an eccentric weight is rotatable to cause the metal cylinder to vibrate. The cylinder is mounted on one end of a flexible drive which serves to rotate the shaft and hence vibrate the cylinder. When the vibrating cylinder is introduced into, and immersed in, the wet concrete mix or slurry, vibrations, which may be in the region of 10,000 per minute, agitate the slurry to extent sufficient to remove air and voids therefrom.
Concrete is a mixture of cement, sand, and stones. Lime is an ingredient in cement and water is mixed with the components of the mixture to activate the lime and form a mix or slurry. With the reinforcing bars immersed in and surrounded by this poured wet mix or slurry, there is a potential problem in that the reinforcing bars may rust. When a steel bar rusts, it expands, and the expansion of the bar within the dried concrete can cause the concrete to crack. To overcome this problem, it has been practice in the art to envelope the reinforcing bars in a plastic-like coating, most commonly an epoxy, which will protect the steel from wet liquid and hence avoid rusting and the subsequent detrimental consequences thereof. Even so, the placing of a rapidly vibrating vibrator within the slurry creates the risk that the vibrator will chip the plastic coating thereby exposing the encased steel to the wet slurry and the prevention of rusting is not eliminated.